Telephone system



May 7,-1940. c. E. LOMAx TELEPHONE 1SYSTEM Filed Oct. 13, 1958 43Sheets-Sheet l INVENTOR. Elm-'anne E. Lnmax ATTORNEYS.

May 7, 1940- c. E. LoMAx TELEPHONE SYSTEM Filed Oct. 13, 1938 sSmets-sheet 2 IMI @Nb INVENTOR. Elarence E. Lomax ATTORNEYS.

May 7, 1940. c. E. LoMAx TELEPHONE SYSTEM Filed oct. 15, 195s 5Smets-Sheet 3 Sul ' lNvENToR BY a Clarence E. Lomax ATTORNEYS.

u adapted for use in an automatic telephone systhe line is` found by thefinder switch of an idle 50 menta May 7, 1940 l ,2,199,543

UNITED STATT-:s PATENT oFFlcE TELEPHONE SYSTEM jClarence. E. Lomax, OakPark, IIL, assignor to Associated Electric Laboratories, Inc., Chicago,IIL, a corporation of Delaware Application october 13, 193s, serial No.234,751

s1 claims. (ci. 11s-11) The present invention relates to automaticstations associated with the subscriber lines in telephone systems andmore particularly to inr the system. proved line circuits associatedwith the lines Another object of the invention is to provide thereof andto improved combined line and cutin a telephone line circuit an improvedcombined 5 o relays adapted for use in the line circuits line andcut-olf relay which is of simple and 5 thereof. rugged construction andarrangement, and

In an automatic telephone system, usually a which is economical tomanufacture and thorline circuit is individually associated with eachoughly reliable in operation. line thereof, which line circuitconventionally It is a further object of the invention to procomprisesseparate and distinct line, cut-off and vide in a telephone line circuita combined line 10 lockout relays-mounted upon a supporting panel. andcut-off relay including a support, line and These three relays areordinarily so connected cut-oil magnets carried by the support, the lineand arranged that the automatic switches in the magnet being of thetwo-step operating type, and systeml having access to a line arecontrolled in an improved mechanical arrangement for con- 16 accordancewith the various operations thereof trolling the operation of the linemagnet. 15 to set up, by way of the line, outgoing call con- A furtherobject of the invention is to provide nections from and incoming callconnections to a an improved automatic telephone system in subscribersubstation associated with the line, which there are incorporated linecircuits of the and that the line is marked as busy to the autotypedescribed, each including a combined line go matic switches havingaccess thereto in theevent and cut-oli relay of the construction noted.20

a fault appears upon the line. Further these re- The features of thepresent invention are illuslays are so connected and arranged that thetrated as being incorporated inl an automatic automatic switches in thesystem having access telephone system including a plurality of subto theline are controlled in accordance with other scriber lines, some of thelines being of the multig5 operations thereof to set up, by way of theline, party type, each line having a line circuit of the 25 revertingcall connections between two of the type described incorporatingacombined line and subscribersubstations associated with the line,cut-offrelay of the construction noted individuin the event the line isof the multiparty type. ally associated therewith, and a number of find-While line circuits of the type briefly described er-connector links forsetting up connections beabove are entirely satisfactory in operation,they tween the various lines. A number of subscriber 30 are moreexpensive to manufacture and to mainsubstations are associated with eachof the lines tain in service than is desirable, primarily due of themultiparty type; and a distributor of the to the fact that threeseparate and distinct represelective type is provided for the purpose oflays are required in each line circuit in order to assigning the linksto the use of calling ones of render the previously-mentioned servicesby way the lines in a predetermined order. Two differ- 35 of theassociated line. ent forms of the line circuit are illustrated whichAccordingly it is an object of the present inmay be associatedalternatively with each of the vention to provide an improved linecircuit adaptlines in the system. lIn the first form of the ed for usein an automatic telephone system line circuit the line and cut-oitrelays are so con- 40 which comprises line and cut-0E relays, whichnected and arranged that a, calling line is marked 40 two relays are soconnected and arranged that as busy to the connector switches of thelinks the automatic switches in the system are conhaving access theretowhen the associated line. trolled thereby to render, by way of asubscriber is found by the nder switch of an idle one of line with whichthe line circuit is associated, the links having access thereto. In thesecond calling, called and reverting call services to the form of theline circuit the line and cut-oli relays 45 subscriber substationsassociated with the subare so connected and arranged that a calling linescriber line. is marked as busy to the connector switches of It isanother object of the invention to provide the links having accessthereto immediately the an improved line circuit of the type describedcall is initiated on the line and prior to the time tem which iseconomical to manufacture and one of the links having access thereto.'I'he which is positive in operation in order to control combined lineand cut-off relay incorpo-rated in the automatic switches in the systemin a each form of the line circuit comprises a supthoroughly reliablemanner, whereby the desired port, line and cut-off magnets carried bythe u services may be rendered to the subscriber subsupport, a movablecontact actuating member operatively associated with the line magnet, amovablecontzatcty actuating member operatively associated with thecut-ofi magnet, contacts respectively associated with the members, andlatching means for controlling the operation of the first-mentionedmember in two steps.

In accordance with one feature of the inventionrthe line circuit isadapted for use in an automatic telephone system including a lineaccessible to an automatic switch, and comprises, in combination, lineand cut-oil relays, the line relay having rst and second operatedpositions, means responsive to the creation of a calling condition onthe line for causing the line relay to be operated to the iirstposition, means responsive to the seizure of the line by the automaticswitch for causing' the cut-off relay to be operated, means controlledby the operation of the cut-off relay for causing the line relay to beoperated to the second position, and automatic switch control circuitsand line marking circuits governed by the line and cut-of! relays.

In accordance with another feature of the invention the line andcut-offrelays and the automatic switch control and line marking circuitsin the line circuit are so connected and arranged that the automaticswitches in the system are controlled thereby to set up, by way of theline, outgoing call connections from the substations associated with theline, incoming call connections to the subscriber substations associatedwith the line, and reverting call connections between two of thesubscriber substations associated with the line, and that the line ismarked as busy to the remainder of the automatic switches not em-`Jployed in a connection including the line while the connection includingthe line is set up, and that the line is marked as busy to the automaticswitches in the event a fault appears thereon.

In accordance with another feature of the invention the line circuitalso comprises means responsive to the creation of a calling conditionon the line for causing theline relay to be operated to the rstposition, means responsive to the seizure of the line by one of theautomatic switches for causing the cut-oil' relay to be operated, meanscontrolled by the operation of the cut-off relay for causing the linerelay to be operated to the second position, means for releasing the oneautomatic switch, means responsive to the release of the one automaticswitch for causing the cut-off relay to be restored, and means forcausing the line relay to remain operated to the second positionsubsequent to the restoration of the cut-off relay in the event acalling condition remains on vthe line. Furthermore, means is providedwhich is controlled, when the line relay is operated to the secondposition and the cut-off relay is restored, for marking the line as busyto the automatic switches.

In accordance with a further feature of the invention a telephone systemis provided which comprises a line, a plurality of l'subscribersubstations associated with the line, a number of automatic switcheshaving access to the line, and a. line circuit of the type describedassociated with the line. Further the telephone system comprises meansresponsive to the initiation of a call at a calling one of thesubstations for creating a calling condition on the line, meansresponsive to the creation of a calling condition on the line forcausing the line relay to be operated to the rst position, meanscontrolled by the operation of the line relay to the first position i'orcausing an idle one of the automatic switches to seize the line, meansresponsive to the seizure of the line by the one automatic switch forcausing the cut-oil. relay to be operated, and means controlled by theoperation of the cut-oil' relay for causing the line relay to beoperated to the second position. Furthermore, the telephone systemcomprises impulse responsive means operative to cause ringing current tobe projected by way of the one automatic switch over the line subsequentto the termination of the calling condition thereon and to cause thecut-oit relay to remain operated, means responsive to the answering ofthe call at a called one of the substations for causing the oneautomatic switch to be released and for creating a new calling conditionon the line, means responsive to the release of the one automatic switchfor causing the cut-oil relay to be released, means responsive to thecreation of the new calling condition on the line for causing the linerelay to remain operated to the second position subsequent to therestoration of the cut-ofi' relay, and means controlled, when the linerelay is operated to the second position and the cut-ot! relay Visrestored, for marking the line as busy to the i automatic switches.

In accordance with a further feature of the invention a telephone systemis provided which comprises a line, a number of inder and connectorswitches having access to the line, and a line circuit of the typedescribed associated with the line. Also, the telephone system comprisesmeans controlled by the operation of the line relay to the irst positionfor marking the line as busy to the connector switches and for causingan idle one of the connector switches to seize the line, and additionalnder and connector switch control circuits and additional line markingcircuits governed by the line and cut-off relays.

In accordance with a further feature of the invention a combined lineand'cut-oi relay is provided which is adapted for use in a telephoneline circuit, and comprises, in combination, a support, line and cut-offmagnets carried by the support and each provided with an energizingwinding, a movable contact actuating member operatively associated withthe line magnet and having a normal position, a movable contactactuating member operatively associated with the cut-o magnet and havinga. normal position, contacts respectively associated with the members,

mechanical means for limiting the movement of the first-mentioned memberaway from its normal position, and means controlled by the energizationof the cut-01T magnet winding for controlling the release of themechanical means. The mechanical means is so constructed and arrangedthat the first-mentioned member is moved a limited distance away fromits normal position in response to the energization of the line magnetwinding prior to the energization of the cut-of! magnet winding, andthat the first-mentioned member is moved a further distance away fromits normal position in response to the energization of the line magnetwinding subsequent to the energization of the cut-off magnet winding.

Further features of the invention pertain to the particular arrangementof the circuit elements thereof, whereby the above-outlined andadditional features are attained.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. The invention,

both as to its organization and method of operation, together. withfurther objects. and advantages thereof, will best be understood byreference to the following specification taken in connection with theaccompanying drawings in which Figs. 1 and 2 taken together illustratediagrammatically a telephone. system including two improved forms ofline circuitsl and embodying the present invention; Fig. 3 is a frontelevational view of a combined line and cut-oi relay adapted to beincorporated into each of the line circuits shown in Fig. 1 andembodying the present invention; Fig. 4 is a side elevational view,partly broken away, oi the relay shown in Fig. 3; Fig. 5 illustratesdiagrammatically the arrangement of the switch springs associated withthe combined line and cut-off relay when it is incorporated in the linecircuit shown on the left-hand side of Fig. 1; and Fig. 6 illustratesdiagrammatically the arrangement of the switch springs associated withthe combined line and cut-olf relay when it is incorporated in the linecircuit shown on the right-hand side of Fig. 1.

Referring now more particularly to Figs. 1 and 2 of the drawings, thetelephone system there illustrated comprises an exchange having a plu-`rality of subscriber lines including the subscriber lines |50 and |60terminating thereat, and provided with a plurality of finder-connectorlinks including the link for setting up connections between the varioussubscriber lines. Also a distributor |03 is provided for assigning idleones of the links to the use of calling ones of the subscriber lines;and a number of reverting call switches, including the reverting callswitch 200, are provided for the purpose of projecting code ringingcurrent over a subscriber line when a reverting call is initiatedthereon. More specifically, the exchange has an ultimate capacity of onehundred lines, and the number of links is determined by the amount oftrailic which the exchange is required to handle, usually ten linksbeing adequate to render satisfactory service.

Each of the links may be identical to the link |00 which comprises afinder portion or switch |0| and a connector portion or switch |02, eachhaving access to each subscriber line in the system. The nder switchandthe connector switch included in each link may be one of any of a numberof Well-known types. However, it is preferable that each of theseswitches includes a. switching mechanism of the Strowger type and theusual control apparatus therefor, the wipers of the switching mechanismincluded in the iinder switch 0| being illustrated at |80, |8| and |82,and the wipers of the switching mechanism included in the connectorswitch |02 being illustrated at |83, |84, and |85. Also the connectorswitch |02 comprises impulse responsive apparatus of any desired typefor projecting code ringing current over an idle called subscriber lineafter it has been seized by the switching mechanism included therein,which is so connected and arranged that a divided ringing circuit may beemployed in the system. The distributor |03 may be one of any of anumber of well-known types. However, it is preferable that thedistributor |03 is of the preselective type, such that an idle link isselected to be assigned to the use of a calling line prior to theinitiation of a call on the line.

At least a number of the subscriber lines terminating at the exchangeare of the party type, the subscriber lines |50 and |80 being partylines, each serving a number of subscriber substations, respectively,including the subscriber substations A, B and C, D. Each of thesubscriber substations is provided with a telephone instrument, a. dialmechanism, and a ringer. The/subscriber substatlons associated with eachparty line are arranged in two groups, the ringer at each substation inthe first group being connected between one line conductor of thesubscriber line and. ground, and the ringer at each substation in thesecond group being connected between the other line conductor of thesubscriber line and ground, whereby a divided ringing circuit isemployed in the system.

A line circuit is individually associated with each subscriber line inthe system, the line circuit |04 being individually associated with thesubscriber line |50, and the line circuit |05 being individuallyassociated with the subscriber line |60. As previously noted, twodifferent forms of line circuits may be alternatively employedV in thesystem, the line circuit |04 being a line circuit of the rst form, andthe line circuit |05 being a line circuit of the second form. Each ofthe line circuits of the rst form may be identical to the line circuit|04 which comprises a combined line and cut-off relay of theconstruction shown in Figs. 3 and 4 including a line magnet or relayRI20, a cut-off magnet or relay RI l0, and al switch spring assembly ofthe Aconstruction and arrangement shown in Fig. 5. Each of the linecircuits of the second form may be identical to the line circuit |05which comprises a combined line and cut-off relay of the constructionshown in Figs. 3 and 4 including a line magnet or relay R|30, a cut-oimagnet or relay Rl40, and a switch spring assemblyof the con' structionand arrangement shown in Fig. 6.

Each of the reverting call switches may be identical to the revertingcall switch 200 which comprises two minor switches 280 and 290, a linerelay R230, a hold relay R240, two transfer relays R260 and R210, a ringcut-off relay R255, a switching-through relay R220, two control relaysR2| 0 and R250, the control and controlled circuits therefor, anda'transformer 20|. The minor switch 280 comprises two rotary switches28| and 282 provided with contact banks 284 and 286, respectively, andassociated wipers 283 and 285, respectively, a rotary magnet M236 forsimultaneously rotating the wipers of the rotary switches 28| and 282,and a release magnet M231 for releasing the wipers of the rotaryswitches 28| and 282 and for causing these wipers to be returnedv totheir normalpositions. Also two switch springs 234 are associated withthe wipers of the rotary switches 28| and 282, which are actuated intoengagement when these wipers are rotated by the rotary magnet; M236 awayfrom their normal positions. The minor switch 290 comprises two rotaryswitches 29| and 292 provided with contact banks 294 and 290,respectively, and associated wipers 293 and 295, respectively, a rotarymagnet M238 for simultaneously rotating the wipers of the rotaryswitches 29| and 292, and a release magnet M239 for releasing the wipersof the rotary switches 29| and 292 and for causing these wipers to bereturned to their normal positions. Also two switch springs 235 areassociated with the wipers of the rotary switches 29| and 292, which areactuated into engagement when these wipers are rotated by the rotarymagnet M238 away from their normal positions. Also it is'noted that thereverting call switch 200 is connected and arranged to project coderinging current over a calling subscriber line by way of the trunk linewhen a connection is established therebetween by way of an operatedoneof the links, in such a manner that a divided ringingv circuit may beemployed in the system.

\ outwardly extending flange 30| to which a line magnet core 302 and acut-od magnet core 303 are respectively secured by two screws 304 and335, the cores 302 and 303 being arranged in spaced parallelrelationship with respect to each other and to the body portion oi theplate 300.

The body portion of the supporting plate 300 is provided with two spacedapart tabs 306 and 301 arranged adjacent the pole faces of the cores 302and 303, respectively. A supporting bracket 308 carrying a pivot pin 309is suitably secured to the tab 306; and a supporting bracket 3|0carrying a pivot pin 3| I is suitably secured to the tab 301. Anarmature 3I2 is pivotally supported on the pivot pin 309 adjacent thepole face of the core 302; and an armature 3|3 is pivotally supported onthe pivot pin 3I| adjacent the pole face of the core 303. The armature3I2 is provided with a downwardly extending arm 3 I4 having a rearwardlyprojecting finger 3I5 on the outer end dthereof extending through anaperture SIG formed in the supporting plate 300; and the armature 3I3 isprovided with a downwardly extending arm 3I1 havingV a rearwardlyprojecting finger 3|8 extending through an aperture 3I9 formed in thesupporting plate 300. A switch spring assembly 320 comprising aplurality of individual switch springs suitably insulated from eachother and 'from the supporting plate 300 is secured to the rear side ofthe supporting plate, and cooperates with an insulating button 32|carried by the ringer 3|5 in such a manner that the individual switchsprings in this switch spring assembly are actuated into engagement anddisengagement with each other in a predetermined manner, when thearmature 3I2 is rotated about the pivot pin 309. Also a switch springassembly, not shown, comprising a plurality of individual switch springssuitably in'- sulated from each other and from the supporting plate 300is secured to the rear side of the supporting plate, and cooperates withan insulating button carried by the ringer 3I8 in such a manner that theindividual switch springs in this switch spring assembly are actuatedinto engagement and disengagement with each other in a predeterminedmanner, when the armature 3I3 is rotated about the pivot pin 3| I.

A blocking or latching spring 322 is secured, intermediate the endsthereof, to the front side of the supporting plate 300 in a positiondisposed between the cores 302 and 303 by an arrangement comprising aninsulating bushing 323 and a screw 324. One end 325 of the latchingspring 322 is positioned in a recess 326 formed in the edge of the ange30| in order to retain the latching spring in place, and the other end321 of the latching spring 322 entends to a position adjacent thearmatures 3I2 and 3|3. The end 321 of the latching spring 322 isbifurcated; comprising two spaced apart fingers 328 and 329 cooperatingwith two projecting lugs 330 and 33|, respectively, carried by thearmatures 3I2 and 3|3. The ringer 328 constitutes a latching nger and isso constructed and arranged that it normally projects into the path ofmovement of the lug 330 carried by the armature 3I2 when this armatureis rotated in a clockwise direction, as viewed in Fig. 4, about thepivot pin 309, thereby to permit only a limited rotational movement o!the amature 3I2 about the pivot pin 309. 'nie ilnger 320 constitutes atripping ringer and is so constructed and arranged that it normallyprojects into the path of movement of the lug 33| carried by thearmature 3|3 when this armature A is rotated in a clockwise direction,as viewed in Fig. 4, about the pivot pin 3| I. When the armature 3I3isrotated in a clockwise direction about the pivot pin 3I| the lug-33|carried thereby engages the tripping finger 329 and bends the end 321 ofthe latching spring 322 away from the supporting plate 300. thereby tomove the latching iinger 328 out of the path of movement of the lug 330carried by the armature 3I2 in order to allow further rotationalmovement of.I

the armature 3I2 in a clockwise direction about the pivot pin 309. Fromthe foregoing description of the construction and arrangement of thelatching spring 322 it will be understood that when the armature 3I2 isrotated in a clockwise direction about the pivot pin 309 it is initiallyrotated only a predetermined distance, at which time the latching nger328 arrests further ro tation thereof. Subseguently, when the armature3I3 is rotated in a clockwise direction about the pivot pin 3I| thetripping finger 329 releases the latching nger 328, thereby to permitfurther rotation of the armature 3I2 in a clockwise direction about thepivot pin 309.

The line magnet core 302 is provided with a winding arrangement which iseffective, when energized, to attract the armature 3I2, thereby torotate this armature in a clockwise direction about the pivot pin 309;and the cut-oli' magnet core 303 is provided with a winding.arrangementwhich is effective, when energized, to attract the armature 3|3, therebyto rotate this armature in a clockwise direction about the pivot pin 3H.Thus it will be understood that, when the winding arrangement of theline magnet is energized, the armature 3I2 is rotated in a clockwisedirection about the pivot pin 309 a predetermined distance, and thensubsequently, when the winding arrangement of the cut-off magnet isenergized to rotate the armature 3|3 in a clockwise direction about thepivot pin 3| I, the armature 3I2 `is rotated an additional distance inthe clockwise direction about the pivot pin 309. Also, it will beunderstood that the initial rotation of the armature 3I2 is effective tocause a predetermined actuation of the switch spring assembly 320associated therewith, and the further rotation thereof is effective tocause a further predetermined actuation of the switch spring assembly.320; and the rotation of the armature 3I3 is effective to cause apredetermined actuation of the switch spring assembly associatedtherewith. Thus, the line magnet 302 is of the two-step type. A

Referring now more particularly to Fig. 5 of the drawings, it will beobserved that the switch spring assembly associated with the line andcutoff magnets RI20 and RIIO, respectively, corresponding to the switchspring assembly incorporated in the line circuit |04, is so constructedand arranged that, when the line magnet RI20 is energized, the armatureindicated at 3I2a is rotated in a clockwise direction about the pivotpin 309a a predetermined distance, thereby to move the switch springRAI28 intoy engagement with the associated switch spring in order toclose these X contacts, and to move the switch spring RAI2I intoengagement with the switch spring RCI22 in order to close these Xcontacts, at which time the outer end of the armature 3| 2a engages thelatching ringer 328a.

Subsequently, when the cut-oli magnet Rl I0 is energized the armatureindicated at 3|3a is rotated in a counterclockwise direction about thepivot pin 3| la, thereby to move the switch springs RAI I2 and RCI I3into disengagement. to move the switch springs RAI I2 and RCI I4 intoengagement, to move the switch springs RAI I5 and RAIIG into engagement,and then to move the' switch springs RAI I6 and RCI I'I intodisengagemove the switch springs RA|23 and RC|24 into disengagement, tomove the switch springs RA|25 and RA|2B into engagement, and then tomove the switch springs RAI26 and RCIZ'I into disengagement.

Referring now more particularly to Fig. 6 of the drawings, it will beobserved that .the switch spring assembly associated with the line andcutoff magnets R|30 and R|40, respectively, corresponding to the switchspring assembly incorporated in the line circuit |05, is so constructedand arranged that, when the line magnet R|30 is energized, the armatureindicated at 3|2b is rotated in a clockwise direction about the pivotpin 30912 a predetermined distance, thereby to move the switch springsRAI33 and RC|33 into disengagement in order to open these X contacts, to'move the switch springs RAI33 and RCI34 into engagement in order toclose these X contacts, to move the switch springs RA|3| and RCI 32 intoengagement in order to close these X contacts, and to move the switchspring RAI3'I into engagement with the associated switch v,

spring in order to close these X contacts, at which time the outer endof the armature 3| 2b engages the latching iinger 32817. Subsequently,when the cut-oli magnet'RI40 is energized the armature indicated at 3|3bis rotated in a counterclockwise direction about the pivot pin 3| Ib,thereby to move the switch springs-RAIN and RCI43 into engagement, tomove the switch springs RAIM and RC|45 into engagement, to move theswitch springs RANG and RAIN into engagement, and then to move theswitch springs RAIIIB and RCI48 into disengagement, to move the switchspring RAME and the associated switch spring into disengagement, to movethe switch spring RA|40' and the associated switch spring intodisengagement, and iinally to move the switch spring RA|4| and theassociated switch spring into disengagement in order to open these Ycontacts. Also when the armature 3I3b is rotated in a counterclockwisedirection about the pivot pin 3||b, the tripping finger 3291) is engagedby the outer end of the armature 3|3b, thereby to release the latchingfinger 328D. The armature 3I2b is then rotated a further distance in theclockwise direction about the pivot pin 30911, thereby to move theswitch spring RA|38 and the associated switch spring into disengagement,to move the switch spring RAI39 and the associated switch spring intoengagement, to move the switch spring RAI30' and the associated switchspring into disengagement, and to move the switch springs RA|36 andRC|35 into disengagement.

The connection and arrangement of the system will best be understoodfrom a consideration of the following description, with reference toFigs. 1 and 2 of the drawings, of the operation of the apparatusincorporated therein to set up the different connections between thevarious subscriber lines.

A call which is to be extended from the subscriber substation A to thesubscriber substation C is rst initiated at the substation A by removingthe receiver of the telephone instrument thereat from its hook, therebyto complete a bridge path at the telephone instrument at the substation-A between the line conductorsCIBI and C|52 of the subscriber line |50extending to the substation A. When this bridge path is completedbetween the line conductors of the subscriber line |50 a bridge circuitis completed for energizing in series the upper and lower windings ofthe line magnet RI20 in the line circuit |04 individually associatedwith the subscriber line |50, which extends from battery at the upperwinding of RI20 by way of the upper winding of RI20, RAIII, CI5I, thebridge path at the substation A between CI5| and CI52, CI52, RCI I1, RAII6, and the lower winding of RI20 to ground. When energized over theabove-traced circuit the line magnet RI20 partially operates, thereby toclose the X contact associated with the switch springs RA|2| and RCI22and to close the X contact associated with the spring RAIN and theassociated switch spring, further actuation of the switch springsassociated with the line magnet RI20 being positively prevented, at thistime, by the mechanical locking arrangement under the control of thecut-0E magnet RIIO. More particularly, the line magnet RI20 completes,at RAI28, a path for applying ground potential to the start conductor C|extending into the distributor |03, this path extending from ground, atRAI26, by way of RCIZ'I, RAI28, and CISI to the start conductor C|90.This application of ground potential to the start conductor C|90initiates the operationof the distributor |03, and causes thedistributor to operate and assign the previously selected idle link tothe use of the calling subscriber line |50. Assuming that theAillustrated link |00 is assigned by the distributor |03 to the use ofthe calling subscriber line |50, the distributoralso marks with groundpotential by way of the conductor C|03 the level in the contact bank ofthe Strowger mechanism included in the finder switch |0I, wherein thecalling subscriber line |50 terminates. Also the linemagnet RI20completes, at RA|2I and RCI22, a path for applyingV battery potential tothe control conductor CI53, this path extending from battery at thewinding of the cut-off magnet RI I0 by way of the winding of RIIO,RAI23, RCI24, RCI22, and RAI2I to the control conductor CI53. Thisapplication of battery potential to the control conductor C|53 marks theradial position of the contact set in the level in the contact bank ofthe Strowger mechanism included in the finder switch |0I, wherein thecalling subscriber line |50 terminates.

The Strowger mechanism included in the finder switch |0| then operatesto move the wipers |00, |8I, and |82 thereof in the vertical directionto the level wherein the calling subscriber line |50 terminates. ThisStrowger mechanism then operates to move the wipers thereof in theradial direction to the radial position of the contact set wherein thecalling subscriber line |50 terminates, at which time the Wipers |00 and|82 application of ground potential to the wiper |8| completes a circuitfor energizing the cut-olf magnet RIIO, this circuit extending from thegrounded wiper |8I by way of the contact terminating the controlconductor C|5 3,l RAIZI, RCI22, RCIZA, `RA|23, and the winding of RI| tobattery. Also this application of ground potential to the wiper I8Icompletes a path for applying ground potential to the control conductorC|54 of the subscriber line |50 extending to the contact banks of theStrowger mechanisms included in the connector switches of the linkshaving access thereto, thereby to mark the subscriber line |50 as busyto the connector switches of these links` This path extends from thegrounded control conductor C|53 by way of.

RA|2I and RC|22 to the control conductor CI54.

Whenenergized over the above-traced circuit the cut-oi magnet RI I0operates to complete, at RAI I5 and RAI I6, an obvious holding circuitfor energizing in series the upper and lower windings of the line magnetR|20, and interrupts, at'

RAIIB and RCIII, and at RAIII, points in the original bridge circuit forenergizing the windings of the line magnet RI20, thereby to free theline conductors CI5| and CI52 of the subscriber line releases thelocking arrangement associated with the armature of the line magnet RI20, thereby to alllow the line magnet RI20 to operate fully. Upon fully"operating, the line magnet R|20 interrupts, at RA|23 and RCI24, a pointin the original circuit for energizing the winding of the cut-off magnetRI I0, and interrupts, at RAI26 and RCI2'I, a point in the path forapplying ground potential to the start conductor C|90 extending to thedistributor |03. When ground potential is removed from the startconductor CIBO the distributor |03 operates to select an idle link inthe group of links to be assigned to the use of the next callingsubscriber line. When the nder switch |0| seizes the calling subscriberline I 50, the connector switch |02 operates to condition the Strowgermechanism therein to be responsive to dialed digits.

The subscriber at the substation A then dials the first digit of thedirectory number of the called subscriber line at the dial mechanismthereat, thereby to transmit a rst series of impulses over the loopcircuit extending by way of the subscriber line |50 between thesubstation A and the connector switch |02. Impulse responsive apparatusin the connector switch |02 operates in response to this rst series ofimpulses in order to cause the wipers |83, |84, and |85 of the Strowgermechanism included therein to be moved in the vertical direction to thelevel in the contact bank therein, wherein the called subin acharacteristic manner.

scriber line |60 is terminated. The subscriber at the substation A thendials the second digit of the directory number of the called subscriberline at thel dial mechanism thereat, thereby to transmit a second seriesof impulses by way of the previously mentioned loop circuit to theconnector switch |02 in order to cause the wipers noted of the Strowgermechanism included therein to be moved in the radial direction to theposition of the contact set in the contact bank therein, wherein thecalled subscriber line |60 is terminated. The subscriber at thesubstation A then dials the third digit of the directory number of thecalled substation C at the dial mechanism thereat, thereby to transmit athird series of impulses by way of the previously mentioned loop circuitto the connector switch |02 in order to cause the connector switch toselect a corresponding code ringing current to be projected a over thecalled subscriber line |60 in the event this: subscriber line is idle.,4

At this time the wipers |83 and |85 engage the contacts in the contactbank terminating the line conductors CI6I and CI62, respectively, andthe wiper |84 engages the contact in the contact bank terminating thecontrol conductor CIGS of the called.' subscriber line I 60.. At thistime `ground potential appears upon the control conductor C|63 in theevent the called subscriber line |60 is busy. On the other hand, batterypotential appears upon the control conductor CI63 in the "event thecalled subscriber line |60 is idle.

Assuming that the called subscriber line |60 is busy, ground potentialderived in the line circuit |05 appears upon the control conductor C|63thereof, thereby to complete a path for energizing a busy relay includedin the connector switch |02, which busy relay operates to cause busytone current to be returned over the loop circuit extending to thecalling subscriber substation A, in the usual manner. The production ofbusy tone in the receiver of the telephone instrument, at the callingsubstation A indicates to the subscriber thereat that the desiredconnection cannot immediately be had due to the busy condition of thecalled subscriber line |60. The subscriber at the calling substation Athen releases the operated link |00 and the line circuit |04 byreplacing the receiver of the telephone instrument at the substation Aupon its hook. 'I'he exact manner in which these operated pieces ofapparatus are released is described in detail hereinafter. a

Assuming that the called subscriber line |60 is idle, battery potentialappears upon the control conductor CI63 thereof, this battery potentialbeing derived at the winding of the cut-oil' magnet RI and extendingtherefrom by way of the Winding of RMU, RA|30,RC|33,and RARI tothecontrol conductor CI63. This application of battery potential to thecontrol conductor CI63 completes a path for short-circuiting the busyrelay included in the connector switch |02, thereby to causetheconnector switch |02 to operate and project ringing current of thepreviously selected code over the called subscriber line in order tocause the ringer at the substation C to operate This characteristicoperation of the ringer at the substation C indicates to the subscriberthereat that the substation C is the called substation. Also, aswitch-through relay in the connector switch |02 operates to applydirect ground potential to the Wiper I 8l.

This application of direct ground potential to the u wiper |84 completesa circuit for energizing the cut-oi magnet R|40, this circuit extendingfrom the grounded wiper |84 by way of C|63, RAISS, RC|33, RAI30', andthe winding of R140 to battery. When energized over the above-tracedcircuit the cut-ofi magnet R|40 operates to complete, at RA|44 andRC|45, a holding circuit for energizing the winding thereof, thiscircuit extending from the grounded control conductor CI63 by way ofRAI, RC|45, and the winding of R|40 to battery. Also, upon operating,the cut-oil' magnet R|40 completes, at RA|45 and RAI41, a holdingcircuit for energizing the line magnet R|30, this circuit extending fromground, at the lower winding of R|30, by way of the lower winding ofR|30, RA|46, RAI41, and the upper winding of R|30 to battery. Also, uponoperating, the cut-01T magnet R|40 releases the locking arrangementassociated with the armature of the line magnet R|30, thereby to allowthe line magnet R|30 to operate fully. When energized over theabove-traced circuit the line magnet R|30 fully operates to complete, atRAI 3| and RC|32. a path for applying ground potential to the controlconductor C|64 of the subscriber line |60 extending to the contact banksof the Strowger mechanisms included in the finderl switches of the linkshaving access thereto, thereby to mark the subscriber line |60 as busy,this path extending from the grounded control conductor C|63 by way ofRC|43, RA|42, RC|32, and RA|3| to the control conductor C|64. Thesubscriber at the substation C then answers the call by removing thereceiver of the telephone instrument thereat from its hook, thereby tocause the connector switch |02 to operate in order to interrupt theprojection of ringing current over the called subscriber line and tocomplete an established communication connection between the callingsubscriber line |50 and the called subscriber line |60 by way of theoperated link |00.

Assuming that the release of this established connection is under thecontrol of the last subscriber to replace the receiver of the telephoneinstrument at his substation upon itsA hook, when the last subscriber atone of the substations replaces the receiver of the telephone instrumentthereat upon its hook the operated link is released in the usual manner.thereby to interrupt the established connection extending between thesubscriber lines |50 and |60. When the link |00 is released groundpotential therein is removed from the wiper 8|, thereby to interrupt thepreviously traced holding circuit for energizing the winding of thecut-ofi magnet R||0. The cut-oi magnet R||0 then restores, thereby tointerrupt, at RAI I2 and RCI I4, a further point in the holding circuitfor energizing the winding thereof, and to interrupt, at RAI I5 and RAII5. the previously traced circuit for energizing in series the upper andlower windings of the line magnet R|20. Also, upon restoring, thecut-off magnet R| In prepares, at RA|||, and at RA||6 and RC| I1, thepreviously traced bridge circuit for energizing the windings of the linemagnet R|20. The line magnet R| then restores to complete, at RA|23 andRC|24. the previously traced path for applying battery potential, at thewinding of the cut-off magnet Ri I0, to the control conductor C|54extending to the contact banks of the Strowger mechanisms included inthe connector switches of the links having access thereto, thereby tomark the subscriber line |50 as idle. Also the line magnet R|20prepares, at RA|26 and RCIZ'I, a point in the previously traced path forapplying ground potential to the start conductor C |90, and interrupts,at RAI-28, a point in this path. Finally, the line magnet R|20interrupts, at RA|2| and RC|22, the connection between the control!conductor C|53 and C|54, thereby to .interrupt the paths for applyingground or battery potential to the control conductor C|53 extending tothe contact banks of the Strowger mechanisms included in the finderswitches of the links having access thereto, in order to mark thesubscriber line |50 as idle. At this time the subscriber line |50 ismarked as idle to the iinder and connector switches of the links havingaccess thereto, and the line circuit |04 is completely released.

Also, when the link |00 is released ground potential therein is removedfrom the wiper |84, thereby to` interrupt the previously traced holdingcircuit for energizing the winding of the cut-oil' magnet R|40. Thecut-oil" magnet R|40 then restores, thereby to interrupt at RA|44 andRC| 45, a further point in the holding circuit for energizing thewinding thereof, to interrupt, at

the line-magnet R|30, and prepares, at RAMI,

and at RA|46 and RC|48, pointsin a bridge circuit for energizing thewindings of the line magnet R|30. The line magnet R| then restores tocomplete, at RA|30', and at RA|33 and RC|33, the previously traced pathfor applying battery potential. at the winding of the cut-ofi magnetR|40, to the control conductor C|63 extending to the contact banks ofthe Strowger mechanisms included in the connector switches of the linkshaving access thereto, thereby to mark the subscriber line as idle. Alsothe line magnet R|30 interrupts, at RA|3| and RC|32, the connectionbetween the control conductors C|63 and C|64, thereby to interrupt thepath for applying ground or battery potential to the control conductorC|64 extending to the contact banks of the Strowger mechanisms includedin the finder switches of the links having access thereto, therebyv tomark the subscriber line |60 as idle. At this time the subscriber line|60 is marked as idle to the finder and connector switches of the linkshaving access thereto, and the line circuit |05 is completely released.

A call which is to be extended from the subscriber substation C to thesubscriber substation A is rst initiated at the substation C by removingthe receiver of the telephone instrument thereat from its hook, therebyto complete a bridge path at the telephone instrument at the substationC between the line conductors C|6| and C|62 of the subscriber line |60extending to the substation C. When this bridge path is completedbetween the line conductors of the subscriber line |60 a bridge circuitis completed for energizing in series the upper and lower windings ofthe line magnet R|30 in the line circuit |05 individually associatedwith the subscriber` line |60, which extends from battery at the upperwinding of R|30 by way of the upper winding of R|30, RAMI, C|6 l, thebridge path at the substation C' between CIBI and C|62, Cl62, RC'I48,RAME, and the lower winding of R|30 to ground. When energized over theabove-traced circuit the line magnet R|30 partially operates, thereby toclose the X contact associated with the switch springs RAI3|l and RC|32,to close the X contact associated with the switch springs RA|33 and RC|34 to close the X contact associated with the switch spring RA|3`I andthe associated switch spring, and to open the X contact associated withthe switch springs RA|33 and RC|33. Fur-l ther actuation` of the switchsprings associated with the line magnet RI30 is positively prevented, atthis time, by the mechanical locking arrangement under the control ofthe cut-oil' magnet RMU. More particularly, the line magnet R|30completes, at RAI31, a path for applying ground potential to the startconductor C|90 extending into the distributor, |03, this path extendingfrom ground, at RA|31, by way of RA|38, and C|92 to the start conductorC|90. This application of ground potential to the start conductor C|90initiates the operation of the distributor |03, and causes thedistributor to operate and assign the previously selected idle link tothe use of the i calling subscriber line |60. Assuming that theillustrated link |00 is assigned by the distributor .|03 to the use ofthe calling subscriber line |60,

. path for applying battery potential to the control conductor C|64,this path extending from battery, at the Winding of the cut-01T magnetRMO, by way of the Winding of RMO, RAl30', RC|32, and RAISI, to thecontrol conductor CIM. This application of battery 'potential to thecontrol conductor CIM marks the radial position of the contact set inthe level in the contact bank of the Strowger mechanism included in thefinder switch |0|, wherein the calling subscriber line |60 terminates.Further the line magnet R|30 completes, at RAI33 and RCI, a path forapplying ground potential to the control conductor C|63 extending to thecontact banks of the Strowger mechanisms included in the connectorswitches of the links having access thereto, there- 'by to mark thesubscriber line |60 as busy immediately, and prior to the time theiinder switch |0| of the link |00 operates to seize this subscriberline, this path extending from ground, at RAI36, by way of RCI35, RCI34,and RAI33,`to the control conductor C|63. Finally, the line magnet R|30interrupts, at RA|33 and RC |33, a point in the previously tracedconnection between the control conductor CI63 and the winding of thecut-off magnet RMO, thereby to prevent the application of groundpotential to the control conductor C|63 from causing prematureenergization of the cut-oir magnet RMO prior to the time the iinderswitch |0| operates to seize the calling subscriber line |60.

The Strowger mechanism included in the iinder switch IOI then operatesto move the wipers |80, IBI, and I82'thereof in the vertical directionto the'level wherein the calling subscriber line |60 terminates. 'I'hisStrowger mechanism then operates to move the wipers thereof in theradial direction to the radial position of the contact set wherein thecalling subscriber line |60 terminates, at which time the Wipers and |82thereof engage the contacts terminating the line conductors C|6| andCl62, respectively, and the wiper |8| engages the contact terminatingthe control conductor CIBG of the calling subscriber line |60. Thepresence of battery potential upon the control conductor C|64 completesa circuit' for energizing a relay in the iinder switch 0| operative toarrest further operation of the Strowger mechanism included therein,which relay also operates to complete a path for applying groundpotential to the wiper IBI. I'I'his application of ground potential tothe wiper |8| completes a circuit for energizing the cut-off magnet RMD,this circuit extending from the grounded wiper |8| by way of the contactterminating the control conductor C|64, RAIBI, RCI32, RAI30', and-thewinding of RMD to battery. g

When energized over the above-traced circuit the cut-off magnet RMUoperates to complete, at RAM2 and RCM3, and at RAM4 and RCMS, a holdingcircuit for venergizing the winding thereof, this circuit extending fromthe grounded control conductor C|64 by way of RAI3I, RCI, RAM2, RCM3,RAI, RCMS, and the winding of R|40 to battery. Also the cut-ofi' magnetRMO completes, at RAMZ and RCM3, a connection between the controlconductors CI|i3` and CI64, thereby to complete a path for applyingground potential appearing upon the control conductor C|64 to thecontrol conductor C|63 extending to the contact banks of the Strowgermechanisms included in the 'connector switches ofthe links having accessthereto, this path extending from the control conductor C|64 by way ofRAIII, RC|32, RAM2, and RCIII3, to the control conductor C|63. This pathfor applying ground po-J tential tothe control conductor C|63 causes thesubscriber line |60 to be marked. as busy to the connector switches ofthe links having access thereto after the line magnet R|30 operatescompletely to interrupt, at RAI36 and RC|35, the previously traced pathfor applying ground potential to the control conductor Cl63. Also thecut-oil. magnet R|40 completes, at RAME and RAM1, the holding circuitfor energizing in series y the upper and lower windings of the linemagnet R|30, this circuit'extendingfrom ground, at the lower winding ofR|30, by way of the lower winding of R|30, RAMS, RAM1, and the upperwinding of RI30 to battery. Finally, the cut-oil' magnet RMO interrupts,at RAM6 and ROMS, and

at RAMI, points in the original bridge circuit for energizing thewindings of the line magnet R|30, thereby to free the calling subscriberline |60 of impedance elements. Also, upon operating, the cut-ofi'magnet RI40 releases the locking arrangement associated with thearmature of the line magnet R|30, thereby to allow the line magnet RI30to operate fully. Upon fully operating, the line magnet RI30 interrupts,at RAI30, a point in the original circuit for energizing the winding ofthe cut-oil magnet RMU, and interrupts, at RA|38, a point in the pathfor applying ground potential to the start conductor CI extending to thedistributor |03. When ground potential is removed from the startconductor CI90 the distributor |03 operates to select an idle link inthe group of links to be assigned tothe use of the next callingsubscriber line. Also, upon operating, the line magnet R|30 interrupts,at RA|36 and RCI35, a point in the original path for applying groundpotential, at RAISS, to the control conductor C|63 extending to thecontact banks of the Strowger mechanisms included in the connectorswitches of the links having access thereto, ground potential beingapplied to the control conductor C |63 at this time by way of thepreviously traced path from the control conductor CIM. When the iinderswitch IOI seizes ,the calling subscriber line |60, the connector switch|02 operates to condition the Strowger mechanism therein to beresponsive to dialed digits. f

'Ihe subscriber at the substation C then dials the rst digit of thedirectory number of the called subscriber line at the dial mechanismthereat, thereby to transmit a ilrst series of lmpulses over the loopcircuit extending by way of the subscriber line |60 between thesubstation C and the connector switch |02. Impulse responsive apparatusin the connector switch |02 operates in response to this iirst 'seriesof impulses in order to cause the wipers |83, |84, and |85 of theStrowger mechanism included therein to be moved in the verticaldirection to the level in the contact bank therein, wherein the calledsubscriber line |50 is terminated. The subscriber at the substation Cthen dials the second digit o1' the directory number of the calledsubscriber line at the dial mechanism thereat, thereby to transmit asecond series of impulses by way of the previously mentioned loopcircuit to the connector switch |02 in order to cause the wipers notedof the Strowger mechanism included therein to be moved in the radialdirection to the position of the contact set in the contact banktherein, wherein the called subscriber line I 50 is terminated. Thesubscriber at the substation C then dials the third digit of thedirectory number of the called substation A at the dial mechanismthereat, thereby to transmit a third series of impulses by way of thepreviously mentioned loop circuit to the connector switch |02 in orderto cause the 'connector switch to select a corre-- sponding code ringingcurrent to be projected over the called subscriber line |50 in the eventthis subscriber line is idle.

At this time the wipers |83 and |85 engage the contacts in the contactbank terminating the line conductors C|5I and CI52, respectively, andthe wiper |84 engages the contact in the contact bank terminating thecontrol conductor CI54 of the called subscriber line 50. At this timeground potential appears upon the control conductor C |54 in the eventthe called subscriber line |50 is busy. On the other hand, batterypotential appears upon the control conductor C|54 in the event thecalled subscriber line I 50 is idle.

Assuming that the called subscriber line |50 is busy, ground potentialderived in the line circuit |04 appears upon the. control conductor CI54thereof, thereby to complete a path for energizing the busy relayincluded in the connector switch |02, which busy relay operates to causebusy tone current to he returned over the loop circuit extending to thecalling subscriber substation C, in the usual manner. The production ofbusy tone in the receiver of the telephone instrument at the callingsubstation C indicates to the subscriber thereat that the desiredconnection cannot immediately be had due. to the busy condition of thecalled subscriber line |50. The subscriber at the calling substation Cthen releases the operated link and the line circuit |05 by replacingthe receiver of the telephone instrument at the substai-ion C upon itshook. The exact manner in which these operated pieces of apparatus arereleased is described in detail hereinafter.

Assuming that the called subscriber line |50 is f idle. batterypotential appears upon the control conductor C|54 thereof. this batterypotential being derived at the winding of the cut-oil' magnet RI In andextending therefrom by way ofthe winding of RI I0, RAI23, and RCI24 tothe control conductor Cl54. This application ofbattery potential to thecontrol conductor C|54 completes a path for short-circuiting the busyrelay included in the connector switch |02, thereby to cause theconnector switch |02 to operate and project ringing current of thepreviously selected code over the called subscriber line |50 in order tocause the ringer at the substation A to operate in a characteristicmanner. This characteristic operation of the ringer at the substation Aindicates to the subscriber thereat that the substation A is the calledsubstation. Also, 4the switch-through relay ln the connector switch |02operates to apply i direct ground potential to the wiper |84. 'I'hisapplication of direct ground potential to the wiper |84 completes acircuit for energizing the cut-oi magnet RI I0, this circuit extendingfrom the grounded wiper |84 by way of CI 54, RCI 24, RAI 23, and thewinding of RI I0 to battery.

When energized over the above-traced circuit the cut-off magnet RI I0operates to complete, at RAI I2 and RCI I4, a holding circuit forenergizing the Winding thereof, this circuit extending from the groundedcontrol conductor CI54 by way of RAI |2, RCI I4, and the winding of R||0 to battery. Also, upon operating, the cut-off magnet R||0 completes,at RAI and RAI I6, the holding circuit for energizing the line magnetR|20, this circuit extending from ground at the lower winding oi' RI 20by way of the lower winding of R|20, RAI I8, RAI I5, and the upperwinding of R|20 to battery. Also, upon operating, the cut-oi magnet RII0 releases the locking arrangement associated with the armature of theline magnet RI 20, thereby to allow the line magnet RI20 to operatefully. When energized over the above-traced circuit the line magnet R120fully operates to complete, at RAI2| and RCI22, a path for applyingground potential to the control conductor C|53 of the subscriber line|50 extending to the contact banks of the Strowger mechanisms includedin the finder switches of the links having access thereto, thereby tomark the subscriber line |50 as busy, this path extending from thegrounded control conductor CI54 by way of RCI 22 and RA|2| to thecontrol conductor CI53. The subscriber at the substation A then answersthe call by removing the receiver of the telephone instrument thereatfrom its hook, thereby to cause the connector switch |02 to operate inorder to interrupt the projection of ringing current over the calledsubscriber line and to complete an established communication connectionbetween the calling subscriber line |60 and the called subscriber line|50 by way of the operated link |00.

'I'he release of this established connection is under the control of thelast party to replace the' receiver of the telephone instrument at hisstation upon its hook, as previously assumed; and the exact manner inwhich the operated link I 00 and the operated line circuits |05 and |04,respectively, individually associated with the subscriber lines |60 and|50 are released is the same as that previously described.

A reverting call which is to be extended from the subscriber substationA to the subscriber substation B is first initiated at the substation Aby removing the receiver of the telephone instrument thereat from itshook, thereby to complete the previously traced bridge circuit forenergizing in series the windings of the line magnet Rl20. When thusenergized the line magnet R|20-par tially operates, as previouslyexplained, thereby to close the ,X contacts associated `with the switchsprings RA|2| and RCI22, and RA|28 and the associated switch spring, inorder to cause battery potential to be applied to the control conductorCI53 and ground potential to be applied to the start conductor C|90, aspreviously noted. This application of ground potential to the startconductor C|90 causes the distributor |03to oper- .conductor CI12.

group of links to the use oi the calling subscriber line |50.

|50, this application of ground potential to the start conductor C|30and this application of battery potential to the control conductor C |53marks the position of the contact set in the contact bank of theStrowger mechanism included in the nder switch IOI at which thesubscriber line .|50 is terminated. The finder switch IOI then operatesin the previously described manner, thereby to seize the callingsubscriber line |50. When the calling subscriber line |50 is seized thecut-oir magnet RI I operates to release the latching arrangementassociated with the armature of the line magnet R|20, and to completethe previously traced holding vcircuit for energizing in series theupper and lower windings of the line magnet RI20 in order to allow theline magnet RI20 to operate fully. At this time the line and cut-oil'magnets RI20 and RI I0 are completely operated, as previously noted.

The connector switch |02 is conditioned to be responsive to a series ofdialed digits at this time. The subscriber at the substation A thendials at the dial mechanism thereatsuccessively two predetermined digitsinto the connector switch |02, thereby to cause the connector switch tooperate and select the rst trunk line terminating-thereat to which anidle reverting call switch is connected. When these two predetermineddigits are successively dialed the connector switch |02 operates as atrunk hunting connector switch in order to select a trunk lineassociated with an idle one of the reverting call switches or to returnbusy tone current over the loop circuit extending to the callingsubscriber substation A in the event that all Vof the reverting callswitches are busy. Assuming that the illustrated reverting call switch200 is the iirst idle switch, the connector switch- |02 operates toseize the trunk line extending thereto. The reverting call switch 200 ismarked as idle or busy, respectively, by thepresence of battery orground potential upon the control conductor CI12 of the trunk line |10.At this' time, the reverting call switch-200 being idle, batterypotential appears upon the control conductor CI12 of the trunk line |10`the path for connecting battery potential to the control conductor CI12extending from battery at the resistor 206 by way of the resistor 206,RA21I, RC242. RA24I, and RA256 to the control When the connector switch|02 selects the trunk line |10 extending to the idle reverting callswitch 200, further operation thereof is arrested due to the presence ofbattery potential upon the control conductor CI 12'thereof, in the usualmanner.A

When the trunk line |10 is thus seized by the connector switch |02, thisconnector switch operates to complete a. loop circuit between thecalling subscriber substation A and the line relay R230 in the revertingcall switch 200, this loop circuit extending from ground at the lowerwinding of R230 by way of the lower winding of R230, RC229, and RA221 toCI13, and from battery at the upper winding of R230 by way of the upperwinding of R230, RC222, and RA22| to CI1I, the line conductors C|1| andCI13 of the trunk line |10 being connected by way of the operated link|00 to the line conductors CI5I and C|52, respectively, of the callingsubscriber line |50, and the telephone instrument at the substation Abeing included in a bridge path extending between the line conductorsCI5I and CI52 of the subscriber line |50.

Assuming that the illustrated link |00 `is assigned to the use of thecalling subscriber line l 2,199,643 ateand assign a previously selectedidle link in the When energized'over the above-traced circuit the linerelay R230 operates to complete, at RA23| and RC232, an obvious circuitfior energizing the Vhold relay R240. When thusenerglzed `the hold relayR240 operates to interrupt. at RA24| and RC242, a point in the path for'applying battery potential to the control conductorC|12 oi Vthe trunkline |10, and completes, at RA24| and RC243, a path for applying groundpotential to the control conductor-CI12, this path extending fromground, at RC243, by way of .RA24|, and RA256 to the control conductorCI12. This application of ground potential to the control conductor CI12of the trunk line |10 marks this trunk line as busy to the connectorswitches of the links having access thereto, and causes theswitchthrough relay in the connector switch |02 to operate. When theswitch-through relay in the connector switch I 02 operates, groundpotential inthe operated link |00 is removed from the wipers I8I and |34of the iinder and connector switches I 0| and |02,respectively,.thelink|00 and the line circuit |04 being retained in itsoperated position at this time due to the application of groundpotential to the control conductor CI12 of the trunk line |10. Also,upon operating, the relay R240 prepares, at RA245, a point in an impulsecircuit traced hereinafter for energizing the rotary magnets M230 andM238 of the minor switches 280 and 290, respectively, included in thereverting call switch 200. l

'I'he subscriber at the calling substation A then dials at the dialmechanism thereat a third digit corresponding to the last digit of thedirectory number of the calling substation A, thereby to transmit aseries of impulses by way of the previously mentioned loop circuit tothe line relay R230. The relay R230 follows the dialed impulses in theVusual manner, restoring each time the loop circuit is interrupted andoperating each time the loop circuit is completed. Each time the relayR230 restores, it interrupts, at RA23I and RC232, the circuit forenergizing the hold relay R240, and completes, at RA23| and RC233, acircuit for energizing in multiple 'the relay R250 and the rotary magnetM236 of the minor switch 280. The last-mentioned circuit extends fromground, at RA23| by way of RC233, RA245, and RA262 to RC204, one branchof this circuit extending from RC264` by wayA of the winding of R250 tobattery, and the other branch extending from RC264 by way of RA213,RC216, and the winding of M236 to battery. The relays R240 and R250,being of the slow-to-release type, remain operated during impulsing.Each time the circuit for energizing the rotary magnet M230 is completedand interrupted, this magnet operates to drive the wipers 283 and 285 ofthe rotary switches 28| and 282, respectively, included in the minorswitch 280 one step away from their normal positions. When the wipersnoted of the rotary switches 28| and 282 are driven away from theirnormal positions, the switch springs 234 are actuated into engagement,thereby to prepare a circuit traced hereinafter for energizing thetransfer relay R210, this circuit being interrupted at this time, atRA25I, by the operated relay R250. In response to this digit the wipers283 and 285 of the rotary switches 28| and 202,*respectively, are-drivena number of steps away from their normal positions corresponding to thisdialed digit and into engagement with corresponding contacts intheassociated contact banks 284 and 280, respectively.

' At the conclusion of the third digit the line relay R230 reoperates.thereby to interrupt, at RA| and RC233, the circuit for energizing inmultiple the relay R250 and the rotary magnet M236 in order to cause therelay R250 to restore shortly thereafter and to arrest further operationof the rotary magnet M236. Upon restoring, the relay R250 completes, atRAI, the previously mentioned circuit for energizing the transfer relayR210, this circuit extending from ground, at the switch springs 234, byway of the switch springs 234, RA25I, and the winding of R210 tobattery. When thus energized the relay R210 operates to complete, atRA212, an obvious holding circuit for energizing the winding thereof, tointerrupt, at RA213 and RC2'I6, a further point in the previously tracedcircuit for energizing the rotary magnet M236, and to prepare. at RA213and RC214, a point in a circuit traced hereinafter for energizing inmultiple the relay 20 R250 and the rotary magnet M230 of the minorswitch 290.

The subscriber at the calling substation A then dials at the dialmechanism thereat a fourth digit corresponding to the last digit of thedirectory number of the called substation B, thereby to transmit anotherseries of impulses by way of the previously mentioned loop circuit tothe line relay R230. The relay R230 follows the dialed impulses in theusual manner. Each time the relay R230 restores it interrupts, at RA23I'and -RC232, the circuit for energizing the hold relay R240, andcompletes, at RA23| and RC233, the previously mentioned circuit forenergizing in multiple the relay R250 and the rotary magnet M238 of theminor switch 290. The last-mentioned circuit extends from ground, atRA23I, by way of RC233, RA245, and RA262 to RC264. one branch of thiscircuit extending from RC264 by way of the winding of R250 to battery,and the other branch extending from RC264 by way of RA213, RC214, andthe winding of M238 to battery. Each time the circuit for energizing therotary magnet M238 is completed and interrupted, this magnet operates todrive the wipers 293 and 295 of the rotary switches 29| and 292.

respectively, included in the minor switch 290 one step away from theirnormal positions. When the wipers noted of the rotary switches 29| and292 are driven away from their normal positions the switch springs 235are actuated into engagement, thereby to prepare a circuit tracedhereinafter for energizing the transfer relay R260, this circuit beinginterrupted at this time, at RA252, by the operated relay R250. Inresponse to this digit the wipers 293 and 295 of the rotary switches 29|and 292, respectively, are driven a number of steps away from theirnormal positions corresponding to this dialed digit 'and into engagementwith corresponding contacts in the associated contact banks 294 and 296,respectively. At the conclusion of the fourth digit the line relay R230reoperates, thereby to interrupt, at RA23| and RC233, the circuit forenergizing in multiple the relay R250 and the rotary magnet M238 inorder to cause the relay R250 to restore shortly thereafter and toarrest further operation of the rotary magnet M238. Upon restoring, therelay R250 completes, at RA252, the previously mentioned circuit forenergizing the transfer relay R260, this circuit extending from ground,at the switch springs 235, by way of the switch springs 235, RA252, andthe winding of R260 to battery. When thus energized the relay R260operates to complete, at RA26I, an obvious holding circuit forenergizing the winding thereof, to interrupt, at RA262 and RC2, afurther point in the previously traced circuit for energizing inmultiple the relay R250 and the rotary magnet M230, and to prepare, atRA202 and RC263, a circuit traced hereinafter for energizing the relayR2|0.

Shortly after `the conclusion of the fourth digit dialed the subscriberat the substation A replaces the receiver of the telephone instrumentthereat upon its hook, thereby to interrupt the loop circuit extendingto the line relay R230 in order to cause the latter relay to restore.Upon restoring, the relay R230 completes, at RA23| and RC233, thepreviously mentioned circuit for energizing the relay R2l0, this circuitextending from ground,`at RA23I, by way of RC233, RA245, RA262, RC263,RA258, and the winding of R2|0 to battery. When thus energized the relayR2|0 operates to complete, at RA2| I, an obvious path for applyingground potential to the ringing machine start lead C206, to prepare, atRA2I2, a holding circuit traced hereinafter for energizing theswitch-through relay R220, to complete, at RA2I3, a path extending frombattery, at the winding of R220, by way of the winding of R220, RA225,RC226, and RA2|3 to the ring pick-up lead C2|5 for applying batterypotential to C2|5, and to complete, at RA2I4, an obvious holding circuitfor energizing the hold relay R240. The hold relay R240, being of theslow-to-release type, does not restore incident to the restoration ofthe line relay R230, and is retained in its operatedposition over theabove-mentioned holding circuit for energizing the winding thereof.Accordingly, ground potential is not removed from the control conductorC|`|2 of the trunk line |10 incident to the restoration of theline relayR230.

Shortly thereafter and at the beginning of a code ringing cycle, groundpotential is applied in the ringing machine to the ring pick-up leadC2l5, thereby to complete a circuit for energizing the switch-throughrelay R220, this circuit extending from the grounded ring pick-up leadC2I5 by way of RA2I3, RC226, RA225, and the winding of R220 to battery.When thus energized the relay R220 operates to complete, at RA224 andRA225, a holding circuit for energizing the winding thereof extendingfrom ground, at RA2l2, by way of RA224, RA225, and the Winding of R220to battery, and to interrupt, at RA225 and RC226. the original circuitfor energizing the winding thereof by way of the ring pick-up lead C2|5.Also, the relay R220 interrupts. at RA22| and RC222, and at RA221 andRC229, further points in the loop circuit for energizing the line relayR230, and completes. at RA22| and RC223, and at RA221 and RC228, pointsin a circuit traced hereinafter for projecting ringing current from theringing machine associated with the trunk line 206' by way of theoperated reverting call switch 200, the trunk line |10, and the link |00over the subscriber line |50, the exact circuit for projecting ringingcurrent from the ringing machine associated with the trunk line 206 overthe subscriber line depending upon the positions of the wipers of therotary switches included in the minor switches 280 and 290, in a mannermore fully described subsequently.

As previously noted, a divided ringing circuit is employed inthe-system, a first group of sub scriber substations associated witheach party line having ringers thereat connected between one lineconductor of the party line and ground, and a second group of subscribersubstations associated with each party line having ringers thereatconnected between the other line conductor of the party line and ground.The operation of the reverting call switch 200 depends upon whether thecalling and called subscriber substations A and B are in the same group.In the event these subscriber substations are in the same group, thereverting call switch 200 operates to cause ringing current of the codecorresponding to the called subscriber substation to be projected overthe line conductor of the subscriber line |50, to which the ringers ateach of the subscriber substations A and B are connected. In the eventthese subscriber substations are in different groups, the reverting callswitch 200 operates first to cause ringing current of the codecorresponding to the called subscriber substation to be projected overthe line conductor of the subscriber line |50, to which the ringer atthe called substation B is connected, and then to cause ringing currentof the code corresponding to the calling subscriber substation to beprojected over the line conductor of the subscriber line |50, to whichthe ringer at the calling substation A is connected. Also, it is notedthat the subscriber substations associated with the subscriber line |50and having ringers connected to one line conductor thereof are assigneddirectory numbers comprising a third odd digit, and the subscribersubstations associated with the subscriber line |50 and having ringersconnected to the other line conductor thereof are assigned directorynumbers comprising a third even digit.

Assuming that the third digit of the directory number of the callingsubscriber substation A is the No. 1, and the third digit of thedirectory number of the called subscriber substation B is the No. 3, thewipers of the rotary switches of the minor switch 280 engage the firstcontacts in the associated contact banks, and the wipers of the rotaryswitches of the minor switch 290 engage the third contacts in theassociated contact banks. At this time a circuit is completed forprojecting ringing current of the code corresponding to the calledsubscriber substation B over the subscriber `line |50, this circuitextending from the ungrounded terminal of the ringing machine winding byway of the ringing conductor M3, the third contact in the contact bank294 and the associated wiper 293 of the rotary switch 29|, the upperwinding of the ring cut-oil' relay R255, RC223, and RA22I, to the lineconductor C|1| of the trunk line |10, and therefrom by way of theoperated link |00, the line conductor C|5| of the subscriber line |50,and` a condenser and .the ringer at the called substation B, to ground.

Also, a circuit is prepared for energizing the upper winding of the ringcut-off relay R255, which is completed when the subscriber at thesubstation B answers the call by removing the receiver of the telephoneinstrument thereat from its hook, this circuit extending, whencompleted, by way of the previously traced path to the line conductorC|5| of the subscriber line |50, and therefrom by way of the bridge pathat the substation B between the line conductors C|5| and C|52 of thesubscriber line |50, CI52, the operated link |00, the line conductorC|13 of the trunk line |10, RA221, RC228, and the windings 202 and 203of the transionner 20| to ground.

Assuming that the third digit of the directory number of the callingsubscriber substation A is the No. 2, and the third digit of thedirectory number of the called subscriber substation B is the No. 4, thewipers of the rotary switches of the minor switch 280 engage the secondcontacts in the associated contact banks, and the wipers of the rotaryswitches of the minor switch 290 engage the fourth contacts in theassociated contact banks. At this time a circuit is completed forprojecting ringing current of the code corresponding to the calledsubscriber substation B over the subscriber line |50, this circuitextending from the ungrounded terminal of the ringing machine winding byway of the ringing conductor M4, the fourth contact in the contact bank295 and the associated wiper 295 of the rotary switch 292, and thewindings 205 and 204 of the transformer 20| to ground at RA220. Thisringing current traversing the windings 204 and 205 of the` transformer20| induces a corresponding ringing current in the windings 202 and 203thereof, which traverses a path extending from ground by way of thewindings 203 and 202, RC228, RA221, to the line conductor C|13 of thetrunk line |10, and therefrom by way of the operated link |00, the lineconductor C|52 of the subscriber line I 50, and the condenser and theringer at the called substation B to ground. Also, a circuit is preparedfor energizing the upper winding of the cut-of! relay R255, which iscompleted Awhen the subscriber at the substation B answers the call byremoving the receiver of the telephone instrument thereat from its hook,this circuit extending, when completed, from battery at the resistor201, by way of the resistor 201, the second contact in the contact bank284 and the associated wiper 283 of the rotary switch 28|, the fourthcontact in the contact bank 294 and the associated wiper 293 of therotary switch 29|, the upper winding of' R255, RC223, RA22|, the lineconductor C|1| of the trunk line |10, and the operated link to the lineconductor C|5|, and therefrom by way of the bridge path at thesubstation B between the line conductors C|| and C|52 of the subscriberline 50, and a portion of the previously traced circuit to ground, atthe winding 203 of the transformer 20|.

Assuming that the third digit of the directory number of the callingsubscriber substation A is the No. 1, and the third digit of thedirectory number of the called subscriber substation B is the No. 2, thewipers of the rotary switches of the minor switch 280 engage the firstcontacts in the associated contact banks, and the wipers of the rotaryswitches of the minor switch 290 engage the second contacts in theassociated contact banks. At this time a circuit is completed forprojecting ringing current of the code corresponding to the calledsubscriber substation B over the subscriber line |50, this circuitextending from the ungrounded terminal of the ringing machine winding byway of the ringing conductor M2, the second contact in the contact bank296 and the associated wiper 295 of the rotary switch 292, and thewindings 205 and 204 of the transformer 20| to ground at RA220. Thisringing current traversing the windings 204 and 205 of the transformer20| induces a corresponding ringing current in the windings 202 and 203thereof which is projected by way ofthe previously traced path over theline conductor C|52 of the subscriber line |50 to ground at the ringerat the called substation B. Also a circuit is completed for projectingringing current of the code corresponding to the calling subscribersubstation A over the subscriber line |50, this circuit extending fromthe ungrounded terminal of the ringing machine winding by way of theringing conductor MI, the first contact in the contact bank 284 and theassociated wiper 283 of the rotary switch 28|,

the second contact in the contact bank 294'and the associated wiper 293of the rotary switch 29|, the upper winding of the ring cut-off relayR255, RC223, RA22|, the line conductor C|1| of the trunk line |10. theoperated link |00, the line conductor C|| of the subscriber linev |50,and a condenser and the ringer at the calling substation A .to ground.'ihe ringing machine operates to complete the circuits for applyingringing currents to the ringing conductors MI to M5, inclusive,sequentially, thereby to cause the ringer at the called substation B andthe ringer at the calling substation A to be operated alternatively.Also a circuit is prepared for energizing the upper winding of the ringcut-off relay R255,'which is completed when the subscriber at thesubstation B answers the call by removing the receiver of the telephoneinstrument thereat from its hook, this circuit extendinghwhen completed,from the ringing conductor MI by way of the previously traced path toground at the winding 203 of the transformer 20|.

Assuming that the third digit of the directory number of the callingsubscriber substation A is the No. 2, and the third digit of thedirectory number of the called subscriber substation B is the No. 1, thewipers of the rotary switches of the minor switch 280 engage the secondcontacts in the associated contact banks, and the wipers of the rotaryswitches of the minor switch 290 engage the rst contacts in theassociated contact banks. At this time a circuit is completed forprojecting ringing current of the code corresponding to the callingsubscriber substation B over the subscriber line |50, this circuitextending frorn the ungrounded terminal of the ringing machine windingby way of the ringing conductor MI, the iirst contact in the contactbank 294 and the associated wiper 293 of the rotary switch 29|, theupper winding of R255 and a portion of the previously traced circuitincluding the line conductor C|5| of the subscriber line |50 to groundat the ringer at the called substation B. Also a circuit is completedfor projecting ringing current of the code corresponding to the callingsubstation A over the subscriber line |50-, this circuit extending fromthe ungrounded terminal of the ringing machine Winding by way of theringing conductor M2, the second contact in the contact bank 288 and theassociated wiper 285 of the rotary switch 282, the rst contact in thecontact bank 296 and the associated wiper 295 of the rotary switch 292,and the windings 205 and 204 of the transformer 20| to ground, atRA220.` This ringing current traversing the windings 204 and 205 of thetransformer 20| induces a corresponding ringing current in the windings202 and 203 thereof which is projected by way of the previously tracedcircuit including the line conductor C|52 of the subscriber line |50 toground at the ringer at the calling substation A. As previously noted,the ringers at the called and calling subscriber substations B and A,respectively, are operated alternatively. Also a circuit is prepared forenergizing the upper winding of the ring cut-oil relay R255, which iscompleted when the subscriber at the substation B answers the call byremoving the receiver of the telephone instrument thereat from its hook,this circuit extending, when completed, from the ringing conductor MI byway of the previously traced path to ground at the winding 203 of thetransformer 20|.

When the subscriber at the called substation B answers the call, one ofthe previously traced circuits forv energizing the upper winding ofthering cut-o relay R255 is completed, depending upon whether the callingand called substations A and B, respectively, are in the same ordifferent groups, as previously noted. When thus energized the ringcut-oi relay R255 operates to complete, at RA251, a holding circuit forenrgizing the lower winding thereof, this circuit extending from ground,at RA244, by way of RA251 and the lower winding of R255 to battery. Alsothe relay R255 interrupts, at RA256, the previously traced path forapplying ground potential to the control conductor C|12 of the trunkline |10, and interrupts, at RA258; the circuit for energizing the relayR2 0, thereby to cause the latter relay to restore. Upon restoring, therelay R2|0 interrupts, at RA2| the previously traced path for applyingground potential to the ringing machine start lead C206 in order toarrest further operation of the ringing machine associated with thereverting call switch 200, to interrupt, at RA2 I2, the holding circuitfor energizing the relay R220 in order to cause the latter relay torestore, and to interrupt, at `RA2|4, the previously traced holdingcircuit for energizing the hold relay R240. Shortly thereafter the holdrelay R240 restores to interrupt, at RA244, the holding circuit forenergizing the lower winding of the ring cut-off relay R255 in order tocause the latter relay to restore shortly thereafter, and to complete,at RA246, a. circuit for energizing the release magnet M239 of the minorswitch 290, this circuit extending from ground, at RA246, by way ofRA265, RC265, and the winding of M239 to battery. When thus energizedthe release magnet M239 operates to release the wipers of the rotaryswitches 29| and 292 of the minor switch 290, thereby to cause thesewipers to be returned to their normal positions. When the wipers notedof the rotary switches of the minor switch `,290 are returned to theirnormal positions, the

switch springs 235 are actuated into disengagement, thereby to interruptthe holding circuit for energizing the transfer relay R260. The transferrelay R260 then vrestores to interrupt, at RA265 and RC266, the circuitfor energizing the release magnet M239, and to complete, at RA265 andRC261, a circuit for energizing the release magnet M231 of the minorswitch 280, this circuit extending from ground, at RA246, by way ofRA265, lRC261, RA211, and the winding of R231 to battery. When thusenergized the release magnet M231 operates to release the wipers of therotary switches 28| and 282 of the minor switch 280, thereby to causethese wipers to be returned to their normal positions. When the wipersnoted of the rotary switches of the minor switch 280 are returned totheir normal positions, the switch springs '234 are actuated intodisengagement, thereby to interrupt the holding circuit for energizingthe transfer relay R210. The transfer relay R210 then restores ltointerrupt, at RA211, the circuit for energizing A call switch 200operates when the call is answered at the called subscriber substation Bto interrupt, at RAZSB, the path for applying ground potential to thecontrol conductor C| 'I2 of the trunk line |10, thereby to cause thelink |00 to be released and interrupt the holding circuit for energizingthe winding of the cut-oli magnet RI|0 inthe line circuit |04individually associated withy the subscriber line |50. The cut-oitmagnet R| I0 then restores to complete, .at RAI |6 and RCII'l, and atRAIN, a bridge circuit for energizing the windings of the line magnetRI20, thereby to retain this line magnetV in its fully operatedposition. This circuit extends from ground, at the lower winding ofR|20, by way of the lower winding of RI20, RAIIS, RCIII, CI52, thebridge path including the telephone instrument at the called subscribersubstation B between the line conductors C|52 and C|5I of the subscriberline |50, C|5|, RAIII, and the upper winding of RI to battery. Also,upon restoring, the cut-off magnet R||0 interrupts,'`

at RAI I5 and RAI i6, the previously traced holding circuit forenergizing in series the upper and lower windings of the line magnetR|20, interrupts, at RA||2 and RCIM, a 4further point in by way of RA|and RC||3 to RAII2, one

branch of this path extending from RA||2 to CISI, and the other branchextending from RAII2, by way of RC|22 and RAI2I, to CI53. Thisapplication of ground potential to the control conductor CISI, extendingto the contact banks of the Strowger mechanisms included in theconnector switches of the links having access to the subscriber line|50, marks the subscriber line as busy thereto. Also, this applicationof ground potential to the control conductor CI53, extending to thecontact banks of the Strowger mechanisms included in the nder switchesof the links having access to the subscriber line |50, marks thissubscriber line as busy thereto. Due to the fact that the bridge circuitfor energizing the windings of the line magnet R|20 is completed priorto the interruption of the holding circuit for energizing the windingsthereof, as previously noted, the line magnet R|20 remains in its fullyoperated position. At this time the line circuit |04 is operated to lockthe subscriber line |50 out of service; and talking battery is suppliedby way of the previously traced bridge circuit to the telephoneinstrument at the called subscriber substation B.

As previously noted, when the subscriber at the called substation Banswers the call Athe reverting call switch 200 is released, thereby tointerrupt the circuit for projecting ringing current over the subscriberline |50 in order to cause furtherroperation of the ringer-at thecalling subscriber substation A to be arrested. When the operation orthe ringer at the calling subscriber substation A is arrested, thesubscriber thereat is advised that the subscriber at the calledsubstation B has answered the call. The subscriber at the substation A.then removes the receiver of the telephone instrument thereat from itshook, thereby to complete an established connection between the callingand called subscriber substations A and B, respectively, for twowaycommunication therebetween, talking battery being supplied to thesubstation A by way ot the previously traced bridge circuit.

The release of this established connection between the'subscribersubstations A and B is under the control of the last subscriber toreplace the receiver of the telephone instrument at his substation uponits hook. When the last subscriber replaces the receiver of thetelephone instrument at his substation upon its hook, the

bridge circuit for energizing the' windings of the line magnet RI20 isinterrupted, thereby to cause this line magnet to restore completely, aspreviously noted. At thistime the established connection between thesubscriber substations A and B is completely released, and the linecircuit |04 individually associated with the subscriber line |50 isreleased, thereby to mark this subscriber line as idle to the finder andconnector switches of the links having access thereto.

A reverting call which is to beextended from the subscriber substation Cto the subscriber substation D is iirst initiated at the substation C byremoving the receiver of the telephone instrument thereat from its hook,thereby to complete the previously traced bridge circuit for yenergizing in series the windings of the line magthe holding circuit forenergizing the winding of net Rl30. When thus energized the line magnetR| partially operates, as previously exlplained, thereby to close the Xcontacts associated with the switch springs RAISI, RCl32, and RAI33,RCI, and RAI31 and the associated switch spring, and to open the Xcontact associated with the switch springs RAI33, RCI33, in order tocause battery potential to be applied to the control conductor CIE4,ground potential to be applied to the control conductor CIGS, and groundpotential to be applied to the start conductor C|00, as previouslynoted. This application of ground potential to the start conductor C|90causes the distributor |03 to operate and assign a previously selectedidle link in the group of links to the use of the calling subscriberline |60. Assuming that the illustrated link |00 is assigned to the useof the calling subscriber line |60, this application of ground potentialto the start conductor CI90, and this application o! battery potentialto the control conductor Cl, marks the position of the contact set inthe contact bank of the Strowger mechanism included in the iinder switch|0| at which the subscriber line |60 is terminated. The finder switchIOI then operates in the previously described manner, thereby to seizethe calling subscriber line |60. When the calling subscriber line |60 isseized, the cutoi magnet R|40 operates to release the latchingarrangement assoelated with the armature of the line magnet RI30, and tocomplete the previously traced holding circuit for energizing in seriesthe upper and lower windings of the line magnet RI 30 in order to allowthe line magnet Rl30 to operate fully. At this time the line and-cut-off magnets R|30 and R|40 are completely operated, as previouslynoted.

The connector switch |02 is conditioned to be responsive to a sexies ofdialed digits at this time. The subscriber at the substation C thendials at the dial mechanism thereat successively two predetermineddigits into the connector switch |02, thereby to cause this connectorswitch to operate as'a trunk hunting connector switch and seize an idleline in the group of trunk lines extending to reverting call switches inthe event there is an idle reverting call switch in this group, or toreturn busy tone current over the loop circuit extending to the callingsubscriber substation C in the event all of the reverting call switchesin this group are busy. Assuming that the reverting call switch 200 isthe first idle switch in this group, the connector switch |02 operatestoseize the trunk line |10 extending thereto, this trunk line being markedas idle by the presence of battery potential upon the control conductorCH2, in the previously described manner. When the trunk line |10 isseized by the l connector switch |02, further operation of thisconnector switch is arrested, and the reverting call switch 200 isconditioned to be responsive to two series of successively dialeddigits. Also the reverting call switch 200 operates to apply groundpotential to the control conductor C|12 of the trunk line |10, therebyto cause the switchthrough relay in the connector switch |02 to operate.When the switch-through relay in the connector switch |02 operates, aloop circuit is completed between the calling subscriber substation Cand the reverting call switch 200, and ground potential is removed inthe operated link from the wipers |8| and |84 of the inder `andconnector switches |0| and |02, respectively,

the link |00 and the line circuit |05 individually associated with thesubscriber line |60 being retained in their operated positions at thistime due to the presence of ground potential upon the control conductorC|12 of the trunk line |10.v Ihe subscriber at the calling substation Cthen dials successively two digits at the dial' mechanism thereat intothe reverting call switch 200, the third digit dialed corresponding tothe third digit of the directory number of the calling subscribersubstation C, and the fourth digit corresponding to the third digit ofthe directory number of the called subscriber substation D. Thesubscriber at the calling substation C then replaces the receiver of thetelephone instrument thereat upon its hook, and the reverting callswitch 200 then operates, as previously described, thereby to projectringing current over the line conductor of the subscriber line |60 towhich the ringers at the calling and called subscriber substations C andD, respectively, are connected in the event the ringers at both of thesesubscriber substations are included in the same group, and to projectalternately ringing current over the line conductors of the subscriberline |60 in the event thatthe calling and called subscriber substationsC and D, respectively, are included in different groups, as previouslynoted. This ringing current projected over the subscriber line 60 causesthe ringer at the called subscriber substation D to operate in acharacteristic manner, thereby to indicate to the subscriber thereatthat the substation D is the called substation.

The subscriber at the called substation D then answers the call byremoving the receiver of the telephone instrument thereat from its hook,thereby to complete a loop circuit for energizing the upper winding ofthe ring cut-on' relay R255 in the reverting call switch 200 andextending between the substation D and reverting call switch 200. Whenthus energized, the ring cut-o relay R255 operates, in the previouslydescribed manner, thereby to interrupt, at RAZ-56, the path for applyingground potential to the control conductor C|12 of the trunk line |10,and to cause the reverting call switch 200 to be released.

When the path for applying ground potential to the control conductorC|12 of the trunk line is interrupted, the operated link |00 is releasedfor further use, and the holding circuit for energizing the cut-oi!magnet RMU in the line circuit |05 individually associated with thesubscriber line |60 is interrupted, thereby to cause the latter magnetto restore. Upon restoring, the cut-oil' magnet RMO completes, at RAMEand RCMB, and at RAMI, a bridge circuit for energizing the windings ofthe line magnet R|30, this circuit extending from ground, at the lowerwinding of R|30, by way of the lower winding of R|30, RAM6, RCMO, Cl62,the bridge path at the telephone instrument .at the called substation Dbetween the line conductors C|62 and CISI of the subscriber line |60,C|6|, RAMI, and the upper winding of R|30 to battery. Also the cutoffmagnet RMO interrupts, at RAM6 and RAM1, the previously traced holdingcircuit for ener. gizing in series the upper and lower. windings of theline magnet R|30 subsequent to the completion of the above-traced bridgecircuit for energizing these-windings of the line magnet R|30. Thus theline magnet R|30 remains in its fully operated position. magnet RMOinterrupts, at RAI and RCM5, a further point in the holding circuit forenergizing the winding thereof, and interrupts, at RAM2 and RCM3, theconnection between the control kconductor C|63 and the control conductorC|64 of the subscriber line |60. Further, the cut-off magnet RMOcompletes, at RAM9, a path for applying ground potential to the controlconductor C |63, extending to the contact banks of the Further, thecut-off i this path extending from ground, at RA|30, by

scriber line |60 is operated to lock this subscriber Y line out ofservice.

As previously noted, when the subscriber at the called substation Danswers the call, the re.

verting call switch 200 is released, thereby to interrupt the circuitfor projecting ringing current over the subscriber line |60 in order tocause further operation of the ringer at the calling subscribersubstation C to be arrested. When the operation of the ringer at thecalling subscriber substation C is arrested, the subscriber thereat isadvised that the subscriber at the called substation D has answered thecall. The subscriber at the substation C then removes the receiver ofthe telephone instrument thereat from its hook, thereby to complete anestablished connection between the calling and called subscribersubstations C and D, respectively, for two-way communicationtherebetween, talking battery being supplied to the substation C by wayof the previously traced bridge circuit.

'I'he release of this established connection bereplaces the receiver ofthe telephone instrument at his substation upon its hook, the bridgecircuit for energizing the windings of the line magnet RIS!! isinterrupted, thereby to cause this line magnet to restore completely, aspreviously noted. At this time the established connection between thesubscriber substations C and D is completely released, and the linecircuit |05 individually asociated with the subscriber line |60 isreleased, thereby to mark this subscriber line as idle to theiinder andconnector switches of the links having access thereto.

Also it is noted that a. timing arrangement is incorporated in theconnector switch |02 which is operative in the event the switch-throughrelay therein does not operate within a predetermined time interval, dueto the fact that the connector switch has not been fully operated to 29seize a line accessible thereto, to cause ground potential to be removedfrom the Wiper IBI. For

example, the link may be seized in the previously described manner bythe appearance of a fault on one of the subscriber lines, in which casethe connectorswitch |02 thereof would not be operated subsequently toseize a line accessible thereto in order to cause the operation of theswitch-through relay therein, whereby ground potential would be removedfrom the wiper I8 I, as previously noted. Under these conditions whereground potential is removed from the wiper |8|, the holding circuit forenergizing the cut-off magnet in the line circuit associated with theline having the fault thereon is interrupted, thereby to cause thecut-oli magnet to restore. In the event the line having a fault thereonhas a line circuit of the 'connection and arrangement of that of theline circuit |04, the cut-oi magnet therein, corresponding to thecut-oli magnet u RIIO, restores to cause the line to be locked out ofservice in the manner previously described in connection with theextension of a reverting call between the subscriber substations A. andB. In the event the line having a fault thereon has a line circuit ofthe connection and arrangement of that of the line circuit |05, thecut-ofi magnet therein, corresponding to the cut-oli magnet RMU,restores to cause the line to be locked out of service in themanner'previously described in connection with the extension of areverting call between the subscriber substations C and D.

While there have been described what are at present considered to be thepreferred embodiments of the invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modications as fall within the truespirit and scope of the invention.

What is claimed is:

l. A line circuit adapted for use in a telephone system including a lineaccessible to an automatic switch, said line circuit comprising, incombination, line and cut-oi relays, said line relay having a. restoredposition and rst and second operated positions, means responsive to thecreation of a calling condition on said line for causing said line relayto be operated from its restored ,position to its rst operated position,means responsive to the seizure of said line by said automatic switchfor causing said cut-oil relay to be operated, means controlled by theoperation of said cut-off relay for causing said line relay to beoperated to its second operated position, and circuits for controllingsaid automatic switch governed in accordance with the positions of saidline and cut-oil? relays.

2. A line circuit adapted for use in a telephone system including a lineaccessible to an autol matic switch, said line circuit comprising, incombination, line and cut-off relays, said line relay having a restoredposition and iirst and second operated positions, said line relay beingoperative from its restored position to its iirst operated position inresponse to the creation of a. calling condition on said line. meanseective to prevent op eration vof said line relay to its second operatedposition, said cut-oil relay being operative in response to the seizureof said line by said automatic switch, meanscontrolled by the operationoi' said cut-off relay for rendering said lastmentioned meansineffective, whereby said line relay is operated to its second operatedposition, and circuits for controlling said automatic switch` governedin accordance with the positions of said line and cut-oli relays.

3. lA line circuit adapted for use in a telephone system including aline accessible to an automatic switch. said line circuit comprising, incombination, line and cut-ofi relays, said line relay having a restoredposition and iirst and second operated positions, said line relay beingoperative from its restored positionto its rst operated position inresponse to the creation of a calling condition on said line, mechanicalmeans effective to prevent operation of said line relay toits secondoperated position, said cut-off relay being operative in response to theseizure of said line by said automatic switch, means controlled by theoperation of said cut-oli relay for actuating said mechanical means,whereby said line relay is operated to its second operated position. andcircuits for controlling said automatic switch in accordance with thepositions of said line and cut-off relays.

, 4. A line circuit adapted for use in a telephone system including aline provided with at least one line conductor and accessible to anautomatic switch, said line circuit comprising, in combination, line andcut-off relays, said line relay having a restored position and iirst andsecond operated positions, a rst circuit including said line conductorfor said line relay, a holding circuit for said line relay, said iirstcircuit being completed in response to the creation of a callingcondition on said line, whereby said line relay is operated from itsrestored position to its iirst operated position, said cut-off relaybeing operative in response to the seizure of said line by saidautomatic switch, means controlled by the operation of said cut-oirrelay for completing said holding circuit and for interrupting said rstcircuit, whereby said line relay is operated from its rst operatedposition to its second operated position, and circuits for controllingsaid automatic switch governed in accordance with the positions of saidline and cut-oit relays.

5. A line circuit adapted for use in a telephone system including a lineprovided with at least one line conductor and accessible to an automaticswitch, said line circuit comprising, in combination, line and cut-oli'relays, said line relay having a restored position and rst and second operated positions, a iirst circuit including said line conductor for saidline relay, a holding circuit for said line relay, said nrst circuitbeing completed in response to the creation of a calling condition onsaid line, whereby said line relay is operated from its restoredposition to its first operated position, mechanical means eilective toprevent operation of said line relay to its second operated position,said cut-oi relay being operative in response to the seizure of saidline by said automatic switch, means controlled by the operation of saidcut-off relay for actuating said mechanical means, means controlled bythe operation of said cut-oii relay for completing said holding circuitand for interrupting said rst circuit, whereby said line relay isoperated from its rst operated position to its second operated position,and circuits for controlling said automatic switch governed inaccordance with the positions of said line and cut-off relays.

6. A line circuit adapted for use in a telephone system including a linehaving a plurality of subscriber substations associated therewith andaccessible to a number of automatic switches; said line circuitcomprising a circuit network consisting solely of line and cut-offrelays and automatic switch control and line marking circuits governedby said line and cut-oil? relays, said cir; cuit network being soconnected and arranged that said automatic switches are controlled torender by way of said line calling; called and reverting call servicesto said substations, and that said line is marked as busy to theremainder of said automatic switches not employed in rendering a serviceby way of said line while a service is being rendered by way of saidline.

7. A line circuit adapted for use in a telephone system including a linehaving a plurality of subscriber substations associated therewith and[accessible to a number of automatic switches; said line circuitcomprising a circuit network consisting solely of line and cut-ofirelays and cuits governed by said line and cut-off relays; said circuitnetwork being so connected and ai;- ranged that said automatic switchesare controlled to set up by way of said line outgoing call connectionsfrom said substations, incoming call connections to said substations andreverting call connections between two of said substations, and thatsaid line is marked as busy to the remainder of said automatic vswitchesnot employed in a connection including said line while a connectionincluding said line is set up.'

8. A line circuit adapted for use in a telephone system including a linehaving a plurality of subscriber substations associated therewith andaccessible to avnumber of automatic switches; said line circuitcomprising a circuit network consisting solely of line and cut-oi relaysand automatic switch control and line marking circuits governed by saidline and cut-oil relays; said circuit network being so connected andarranged that said automatic switches are controlled to set up by way ofsaid line outgoing call connections from said substations, incoming callconnections to said substations and reverting call connections betweentwo of said substations, and that said line is marked as busy to theremainder of said automatic switches not employed in a connectionincluding said line while a connection including said line is set up,and that said line is marked as busy to said automatic switches in theevent a fault appears thereon.

9. In a telephone system, a line, a number of nder switches and a numberofconnector switches having access to said line, a line circuitassociated with said line and including line and cutof! relays, saidline relay having a restored position and rst and second operatedpositions, means responsive to the creation of a calling condition onsaid line for causing said line relay to be operated from itsrestoredposition to its rst operated position, means controlled by the operationof said line relay to its rst operated position for causing an idle oneof said nder switches to seize said line, means responsive to theseizure of said line by said one finder switch for causing said cut-of!relay to be operated,

means controllecY'by the operation oi said cut off relay for causingsaid line relay t0 be opera ed from its rst operated position to itssecondaperated position, and circuitsv for controlling said connectorswitches governed in accordance with the positions of said line andcut-pff relays.

10. In a telephone system, 'a line. a number ofv nder switches havingaccess t said line, a line circuit associated with said line andincluding line and cut-ofi relays, a distributor associated with saidiinder switches and operative to cause an idle one of said nder switchesto operate and seizey a line marked as a calling line, said line relayhaving a restored position and ilrst and sec ond operated positions,means responsive to the creation of a calling condition on said-line forcausing said line relay to be operated from its restored position to itsfirst operated position, means controlled by the operation of said linerelay to its first operated position for initiating operation of saiddistributor and for marking said line as a calling line, meansresponsive to the seizure of said line by one of said nder switches forcausing said cut-olf relay to be operated, means controlled by theoperation of said cut-oli relay for causing said line relay to be op-/erated from its first operated position to its second operatedposition, and means controlled by automatic switch controland linemarking cirthe operation of said line relay to its second operatedposition for arresting the operation of said distributor.

11. In a telephone system, a line, a number of finder switches havingaccess to said line, a line circuit associated with said line andincluding line and cut-oli relays, a distributor associated with saidfinder switches and operative to cause an idle one of said finderswitches to operate and seize a 1in` marked as a calling line, said linerelay having restored position and rst and second operated positions,means responsive to the creation of a calling condition on said line forcausing said line relay to be operated from its restored position to itsrst operated position, mechanical means effective to prevent operationof said line relay to its second operated position, means controlled bythe operation of said line relay to its rst operated position forinitiating operation of said distributor and for marking said line as acalling line, means responsive to the seizure of said line by one ofsaid iinder switches for causing said cut-oi relay to be operated, meanscontrolled by the operation of said cut-ofi relay for actuating saidmechanical means and for causing said line relay to be operated from itsiirst operated position to its second operated position, and meanscontrolled by the operation of said line relay to its second operatedposition for arresting the operation of said distributor.

12. In a telephone system, a line provided with at least one lineconductor, a number of inder switches having access to said line, a linecircuit associated With said line and including line and cut-off relays,a distributor associated with said nder switches and operative to causean idle one of said iinder switches to operate and seize a line markedas a calling line, said line relay having a restored position and rstand

